Can't Open Engine Source Reference By Widget Reflector

Trying to learn about building plugins with Slate since I’d like to build an editing tool for my game. Seems like following the Widget Reflector references are supposed to be the ways find how things are done with it.

Thing is when I click the references it says it can’t open it because it is references some D:\ drive folder. My computer doesn’t even have a D drive. Any idea how I can fix this? All my engine code is under C:\Program Files\Epic Games\UE_4.17\ . I can try to look it up in visual studio within my project, but that’s a whole lot less convenient when there is a better option.